DE2943797C2 - Method and device for alternating heating and cooling of a heat exchanger - Google Patents

Description

The invention relates to a method according to the preamble of claim 1. It also relates they focus on a heating-cooling system according to the generic term of claim 3.

A method and an apparatus of this type are known, for example, from US Pat. No. 3,556,201 become. Oil is used as the liquid heat transfer medium, the boiling point of which is above the operating temperature lies.

In the case of high-boiling liquids such as oil, the large volumes affect both the containers, the Valves, the pumps and the liquid itself greatly increase the price. High boiling liquids moreover have only about 50% of the specific heat compared to water. With water as a liquid Heat transfer media, the fittings, pumps and tanks can be made a little smaller, here however, the high operating pressure has a detrimental effect on the investment costs.

Apart from the investment costs, the known device is in terms of heat consumption unsatisfactory. In the channels of the heating plates of the press, the distributors, hoses and connecting pipes there are considerable volumes of liquid heat transfer medium which, like the heating plates, are heated and need to be cooled down. A similar proportion is found in the supply and discharge lines to the circulation pump and the diverter valves. The mass of steel for this portion must be additionally heated and be cooled.

The invention is based on the object of reducing the energy consumption in a method of the type mentioned in the introduction to lower. In addition, the investment costs for the device for performing the Procedure to be lowered.

The method according to the invention is characterized by the features of claim Ϊ. An advantageous one The design of this method can be found in claim 2. The inventive device for Implementation of the method is characterized by the features of claim 3.

The method according to the invention is partly with a liquid and partly with a vaporous one Heat carrier worked. This allows the operating pressure of the Keep the system at such a low value that it reduces the investment costs compared to a system can be significantly reduced with water as a heat transfer medium. It should be noted in this context be that the focus of the application of the method according to the invention in heated presses which are heated to 150 to 170 ° C. In order to prevent water from being used at this temperature

jo boiling comes, the system for pressures in the range ate of 22 bar. In the method according to the invention, pressures are depending on the process temperature of 6 to 9 bar is sufficient.

Before the method according to the invention in the last The heating stage is switched to steam as the heat transfer medium, which is in the heat exchanger and in one essential part of the pipeline system existing liquid heat transfer medium in the liquid storage pushed, the for this the .'ichtigc average temperature having. The steam from the steam boiler is expediently used to push it out. After this the liquid heat transfer medium is pushed out, the press is like a known steam-heated one System continues to heat up and in the heating phase the

■ »5 kept at the high temperature for the required time. Due to this procedure, a substantial saving can be made compared to the known method in heat consumption and thus in energy. While, for example, with a usual with Hot water heated system the heat consumption without taking into account the same for both processes The heat requirement for heating plates and product per cycle is 385 KWh, the heat consumption amounts to Implementation of the method according to the invention with a system of the same size to 160.7 KWh per Cycle. In addition, the consumption of electrical energy is reduced from 58 to 19 KWh per cycle.

The invention is explained in more detail by means of two exemplary embodiments with the aid of eight figures. F i g. 1 to 7 illustrate the individual process stages of a first exemplary embodiment, with those for the heat transfer medium in each case lines used are shown reinforced. F i g. 8 represents a second exemplary embodiment.

F i g. 1 illustrates the "Preheat I" step;

F i g. 2 the step »Preheating II«;
F i g. 3 the step »blowing through«;
F i g. 4 the step »heating«;
F i g. 5 the step “precooling I”;

F i g. 6 the step “precooling II”; and F i g. 7 the step »Kuhlen«.

F i g. 8 shows a second embodiment in which two storage tanks work according to the displacement principle.

In the device according to FIG. 1, the heat exchanger is arranged in a multi-opening press 1, which is heated in the course of a working cycle of 40 ⁰ C to 160 ⁰ C, was kept at this temperature and is then cooled again to 40 ° C. A work cycle takes about an hour. A memory 2 for low temperature (75 ° C.), a memory 3 for medium temperature (120 ° C.) and a memory 4 for high temperature (140 ° C.) are provided for this purpose. The reservoirs are connected to a pressurized gas source 5, by means of which the required pressure is ensured in the reservoirs in order to prevent the liquid, in the present case water, from boiling.

Nitrogen is selected as the compressed gas.

The outputs of the memory 2, 3 and 4 are via valves 6, 7 and 8 connected by a line 9 to the feed line 10 to the press, wherein in the line 9 a Pump 11 is arranged as well as a valve 12 upstream of the connection to the supply line 10. The inputs of the memory 2, 3 and 4 are connected to the discharge line 16 of the press 1 via valves 13, 14 and 15. The inputs of the Memory are led down within the memory through pipes 17,18 and 19, so that even with almost empty memory of the heat transfer medium coming from the press 1 below the liquid level in the Memory is supplied.

A heating circuit 20 contains a steam boiler 21, a feed water vessel 21a, a boiler feed pump 21 *, valves 22 and 23 and a condensate drain 24.Instead of the condensate trap 24, the pressureless feed water vessel 21a and the boiler feed pump 21b , an enclosed condensate container can be used to avoid energy losses due to evaporation Condensate return pump can be provided, which conveys the condensate directly into the steam boiler. The heating circuit 20 can be connected to the supply line 10 and the discharge line 16 of the press 1 through the oils 22 and 23. Furthermore, a cooling circuit 25 is provided which, in addition to a cooling tower 26 and a cooling water pump 27, contains two valves 28 and 29.

The operation will now be explained.

It is assumed that the press 1 has a temperature of about 40 ^° C. and that the material to be thermally treated has been introduced into the press. The memories 3 and 4 are full, the memory 2 is empty. All valves are closed.

By opening the valves 7, 12 and 13, the in F i g. 1 fluid path shown by bold lines is formed and the first process step »Preheating I« is initiated. Here the liquid is from the pump 11 is requested from the memory 3 via the press 1 into the memory 2. At the end of the step »Preheat The storage tanks show approximately the specified temperatures and the specified fluid level on.

According to FIG. 2 is then activated by closing the valves 7 and 13 and opening the valves 8 and 14 of the process shown in FIG. 2 The fluid path shown is established and the “Preheating II” step is initiated. At the end of this step have the memories shown in FIG. 2 average temperatures and fluid levels indicated.

It now follows that in FIG. 3 step shown "blowing through". For this purpose, the valves 8 and 12 are closed and the valve 22 is opened. With the Steam from the steam boiler 21 is the water from the press 1 and the lines 10 and 16 in the storage tank 3 pressed, uad so that essential parts of the system are emptied. This step could also be means of

> a separate compressed air source. It is also possible to get this from the press to discharge the expelled water into another of the storage tanks.

After the press has been emptied in this way

in the press in the last heating stage and then To maintain the temperature, steam is supplied as a heat transfer medium. This is in FIG. 4 shown. With the exception of valves 22 and 23, the remaining valves are closed. This means that the fluid cycle is separate from the cycle

1 > of the steam separated.

After the temperature of the press is kept at the high temperature for the prescribed length of time has been initiated, the step "precooling I" is initiated, which is shown in FIG. 5 is shown. Be for this purpose

2 »the valves 22 and 23 are closed and the valves 7, 12 and 15 are open. With the liquid i ^ i the memory 3, the press 1 is cooled without temperature shock in a first cooling step and at the same time the memory 3 is emptied and the memory 4 is filled. F i g. 5 shows

2> the temperature conditions and the water level of the Storage at the end of this process step.

In the following in FIG. 6 process step "Pre-cooling II" is shown by closing the Valves 7 and 15 and opening the valves 6 and 14 the

jo press with the liquid coming from the memory 2 The lower temperature is further cooled and the medium temperature storage tank is filled at the same time. temperature and water levels at the end of this process step are shown in FIG. 6 specified.

In the last process step of cooling, which is shown in FIG. 7 is shown, all memories are again switched off by the press 1 and it is instead by opening the valves 28 and 29 of the cooling circuit 25 formed to the press 1 with the cooling water from the cooling tower 26 to the required low temperature (40 ° C). The thermally treated material is then removed from the press 1.

In the case of the FIG. 1 to 7 illustrated first embodiment the liquid level in the storage tanks changes, and it is increased both when heating and even when cooling, liquid from one storage tank to another via the heat exchanger Storage promoted. The inventive method can, however, also using heating and Perform cooling circuits. This variant is based on FIG. 8 closer he: utters.

In the case of the in FIG. The device shown in FIG. 8 is that of FIG. 1 corresponding parts with one around the number IOC denotes denied number. So much for the function no further explanation is required. Of the three memories 102, 103 and 104, those under the Saving the lowest, a middle and the highest average temperature are assigned all memories except for the memory 104 with the highest average temperature one after the other the press is connected, and the pump 111 calls for the liquid in the circuit from the connected reservoir to the press and back to the attached storage. The memory 104 has a variable liquid level. When the heat exchanger 101 is heated up, liquid is initially between the heat exchanger and the storage 102 lowest temperature, then between the heat exchanger and the storage 103

next higher temperature brought into circulation by the pump 111. Before the last heating stage, the Liquid with the steam of the boiler 121 from the heat exchanger 101 of the press and the part 116 of the line system pressed into the liquid reservoir 104 and then the highest average temperature for further heating and for heating the heat exchanger this steam from the steam boiler fed. When the heat exchanger 101 cools down, it and said part 116 of the line system initially again with liquid from the memory changeable liquid level d h. the memory 104 are filled and the heat exchanger 101 is then first to the memory 103 and then to connected to the memory 102 of the next lower temperature and circulated the liquid. the The following table shows the various valve positions when heating up and cooling down the heat exchanger recognize in the press 101.

106

107

123

128

129

131

135

Preheating I.
Preheating II
Blow through
(Empty press)
Heating / regulating
Fill press
Pre-cooling I
Pre-cooling II
Cool

4- +

opened + closed -

It should also be mentioned that in the exemplary embodiment according to FIG. 8 the pressure maintenance in the storage tank 104 with steam and that for this purpose the memory 104 is connected to the steam boiler 121 via a line 120, a steam pressure reducing valve 132 and a line 133 is connected.

Since the store or stores 102, 103 are fully filled with water, the fluctuation in volume of the system be recorded in memory 104. It is therefore also in a single-stage system, i. H. if when heating up and only one temperature step is inserted when the heat exchanger cools down, a second memory 104 required. The greatest level fluctuation of the memory 104 is due to the fact that at the beginning of the pre-cooling the heat exchanger is empty and must first be filled with water. The memory 104 is about half the size of one of the remaining memories 102 and 103.

As can be seen from the table above, the "blowing through" takes place via line 136 and the changeover valve 135 in the water space of the reservoir 104. As a result

the blowing through and the condensation processes of the vapor cushion in the reservoir 104 on the water surface area increases the volume of the water system. The excess amount of water is drained through a condensate drain 137 and a line 134 fed into the condensate barrel 121a.

Notwithstanding FIG. i also contains the device according to FIG. 8 a cooler 138, which enables indirect cooling of the heat transfer medium. Damii the water used for cooling in the press can no longer be enriched with oxygen and damii cause corrosion and also the deposition of hardness builders (scale) in the Avoid channels of the press.

Although the process and the system are based on a; Heat exchanger were explained in a press, can the heat exchanger can also be part of another device, such as a reaction vessel in which chemical reactions are carried out by alternating: heating and cooling

In addition 8 sheets of drawings

Claims (3)

Patent claims: 1. Method for alternately heating and cooling a heat exchanger, especially for a press or a reaction vessel in which the heat exchanger is gradually filled with liquid of different Average temperatures are heated and then cooled and the liquid is then stored in each case, characterized in that the liquid before the last heating stage is pressed out of the heat exchanger by means of pressurized gas or steam and that the Heat exchanger then for further heating and during the heating stage in which the heat exchanger is kept at a high temperature, steam is supplied. 2. The method according to claim 1, characterized in that the pressurized gas for expelling the liquid Compressed air is used. 3. Device for carrying out the method according to one of claims I and 2, with at least two liquid reservoirs, in which liquid of different average temperatures can be stored, and a line system mt valves, through which the liquid when the heat exchanger is heated from a memory of higher temperature through the heat exchanger a storage of lower temperature and for cooling the heat exchanger a storage of higher temperature can be fed, further with a boiler which can be connected directly to the heat exchanger, characterized in that the boiler is designed as a steam boiler (21, 121) and via the line system Before the last Auiheiz. ° -t-jfe a connection between the steam boiler via the heat exchanger (1, 101) to the store (3, 104) with the highest temperature, which is designed as a store with a variable liquid level, can be established.